The present invention relates generally to fluid seals, and more particularly, to a seal design in which the so-called primary lip and the so-called secondary or auxiliary lip are of a special construction and arrangement to insure improved performance in use as well as greatly facilitated ease of installation. According to the invention, an easier and more reliable installing method is provided, which is made possible by flexing of certain elements of the seal when it is installed.
Prior art fluid seals having both primary and secondary or excluder lips are well known to those skilled in the art. Basically, a "primary lip" is a radially acting seal lip defined in part by fluid and oil side frusto-conical surfaces which meet along a generally circular locus to define the primary seal band. The shaft or other sealed member extends axially through the openings just defined, and the primary seal band portion of the seal body snugly engages the lubricated shaft or the like passing thereto. The seal lip is urged into snug engagement by an annular garter spring in a groove in the primary lip body; this lip retains oil or other fluid on one side of the seal so that it does not leak axially of the shaft even during rotation thereof.
Another portion of the seal body customarily comprises a mass of elastomeric material bonded to a rigid metal or like casing. The casing itself is inserted in a counterbore or other opening in a mechanism to be sealed. The seal thus provides a secondary or static seal with the fixed or relatively immovable part of the sealed mechanism, while both primary and excluder dynamic rotary seals are provided between the relatively movable parts of the mechanism.
In addition to the primary lip, modern oil seals customarily include an "auxiliary", "excluder", or "secondary" lip. This lip is normally also defined by frusto-conical surfaces which meet to define a generally circular seal band, but the excluder lip has a different function and usually is somewhat different construction than the primary lip. Its principal purpose is to engage dust, grit, or another fluid, and prevents such foreign material from entering the space between the two seal bands, and ultimately, the space inside the sealed region. Often, the excluder lip runs either completely dry or relatively free of fluid. In some cases, the shaft being sealed is lubricated by slight weeping or like leakage, or is intentionally lubricated or packed with grease. In any case, it is normally of a larger diameter than the primary lip because its ability to be lubricated and to transfer heat away from the sealed region is impeded by lack of lubricating and cooling fluid.
A consequence of this is that many excluder seals often exclude only relatively larger particles, and even if sized so as to provide a snug interference fit with the shaft, the lack of good dynamic heat transfer paths along the sealed shaft cause the seal to be raised to a high temperature and abraded away rapidly, or embrittled by "post-curing."
Another aspect of known fluid seals is the difficulty involved in installing them, or parts associated with them, in place is their intended environments. During the last several years, there has been a greatly increasing trend towards more compact sealed mechanisms, such as those found on smaller automotive applications. These include front wheel drive transfer case mechanisms, for example.
In these installations, space is at a premium and installation of a seal is a difficult matter. Therefore, potential seal leakage is a serious matter and it is imperative that the seal be kept free from damage during the time it is being installed or when mating parts are being installed with it. Any damage which occurs in seal installation is a serious matter because, even though the seal itself is relatively inexpensive in terms of its own cost, replacement after assembly of the entire mechanism is prohibitively expensive in terms of the labor required to gain access to the seal. In this connection, nicking and gouging of the seal lip during component installation is more common than is desired, and in many cases, seems almost to be an inherent aspect of seal installation.
Still further, the relation between the respective diameters of the primary and secondary lips of the seal is such that installation is often difficult to accomplish without damage, that is, difficult to accomplish reliably according to specifications.
In one particular installation, for example, that of a transfer case, a part of the sealed mechanism is a stub shaft journaled in bearings within a housing having a counterbore in which the seal is installed. Therefore, on the assembly line, it is necessary to insert a mating part into the opening partially closed off by the seal cavity. The part to be inserted is typically a yoke or the like having a splined outer diameter which is to be engaged with a splined inner diameter surface on the stub shaft journaled within the housing. It is required to insert the yoke through the seal diameter from the outside or excluder lip portion of the seal after the seal is installed in the counterbore. Performing this operation or the assembly line creates significant risk of seal damage.
While it is more common to install a seal over a shaft extending out of a counterbore, in which case the primary lip passes over the sealed part first, it is not at all uncommon for a reverse assembly method to be utilized wherein the sealed part passes through the seal from outside the sealed region after the seal is already in place within the counterbore. The present invention is particularly advantageous in such circumstances.
In view of the difficulties of installing fluid seals in certain applications, it is an object of the present invention to provide a seal which is more easily and reliably installed in an intended application than counterpart prior art seals.
A further object of the invention is to provide a seal wherein the primary and secondary lips are joined by a common body center section portion, and wherein this body portion is attached to an annular ring with a radially extending web or flex section which permits relative movement of the primary and secondary lips of the seals relative to the shaft in a predetermined, desired manner.
Another object of the invention is to provide a seal assembly having a composite lip body which includes both primary and auxiliary or excluder lip bodies joined along a center section which is, in turn, affixed to the remainder of the seal body by a radial web section.
A still further object of the invention is to provide a novel seal wherein expanding the primary lip portion of the seal during installation results in a rocking effect which reduces the diameter of the auxiliary sealing lip in a transient manner, and wherein radial compression of the primary lip body results in transiently extending the diameter of the auxiliary or secondary lip.
Yet another object of the invention is to provide an improved method of installing an oil seal having primary and secondary lip portions joined at a central body and connected to the remainder of the seal assembly by a flexible radial web.
Another object of the invention is to provide a shaft seal which is adapted to provide ease of installation and flexibility in use, and in which the flexibility used to accommodate dynamic run out is accommodated principally or largely by a locating element between the seal bonding portion and the lip body, and wherein the seal body as a whole is adapted to rock or "bell-mouth" about such web, whereby radially compression of the primary lip acts to enlarge the diameter of the excluder lip, and radial compression of the excluder lip tends to enlarge the diameter of the primary lip.
Another object of the invention is to provide, in one embodiment of the invention, a radial lip oil seal wherein the seal body includes a relatively short primary lip area and a relatively extended excluder lip, joined by a lip center section forcing an extension of the radial support web, with the web being of relatively thicker cross-section than the cross section of the offsetting section to which it is attached, whereby forces created in inward movement of the primary lip seal band area are able to be transmitted through the body center section to create movement of the excluder lip.
The foregoing and other objects and advantages of the invention are achieved in practice by providing a seal having an annular casing, and an annular seal body disposed therein, with the seal body being subdivided into a bonding portion and a seal lip body portion, with the lip body portion being subdivided into primary and secondary lip units joined to each other along a common seal lip body center section, which in turn is joined to the bonding portion by an annular locating element which includes both an axially extending, flexible offset section and a support web extending radially between the seal body center section and the axially inner end of the flexible offset section.
The exact manner in which the foregoing and other objects and advantages of the invention are achieved in practice will become more clearly apparent when reference is made to the following detailed description of the preferred embodiments of the invention set forth by way for example, and shown in the accompanying drawings, wherein like reference numbers indicate corresponding parts throughout.